1. Field
The application relates to monitoring of internal organs, and more particularly to noninvasive detection of intracorporeal movement and pressure.
2. State of the Art
Intra-corporeal movement can be detected as changes in pressure of a pressure-sensitive detector mounted on the patient's skin over the organ to be monitored. One area in which such methods have been applied is that of preterm monitoring of uterine contractile activity in pregnant women. Uterine activity may be an important predictor of preterm labor (premature delivery) (R. Bell, Brit. J. Obstet. and Gyn. 90:884-887, 1983; Wood et al, Am. J. Obst. & Gynec. 91:396-402, 1965). Measurement of intrauterine pressure is also important for the diagnosis and treatment of difficult labor due to unusually large fetus, abnormal position of fetus, obstructed birth canal, or other factors (Smyth, Brit. J. Obstet. and Gyn. 64:59-66, 1957). A device for measuring intrauterine pressure is sometimes referred to as a tocotonometer or tocodynamometer.
A device for intrauterine pressure monitoring should be noninvasive, reliable, and sensitive to the pressure sought to be measured. It is especially desirable for such a device to be simple enough for a patient to use unassisted at home and comfortable enough to wear for extended periods, while still providing accurate results. It is further desirable that the device not be overly sensitive to motions of the patient which do not relate to uterine contraction.
Many prior intrauterine pressure monitoring devices require a belt which straps the pressure detecting device to the patient's abdomen. For example, devices described by Smyth (ibid) and in U.S. Pat. No. 3,945,373 to Tweed et al each have a flat guard ring with a plunger-like sensor disposed in the central opening of the ring. The guard ring must be pressed firmly against the abdomen by a belt or strap. The plunger is spring mounted and the displacement of the plunger relative to the guard ring reflects the pressure in the abdomen. Plunger displacement may be measured by a variety of types of displacement sensors.
Tocotonometers of this type have a number of disadvantages. For example, accuracy of the measurements depends upon proper placement of the transducer and upon belt tension. Respiratory movements are translated by the belt into pressure compressing the tocotonometer transducer and producing signals unrelated to abdominal contraction. Measurements are quantitative only with regard to the frequency and duration of the contraction, because the signal from the displacement sensor does not quantitatively reflect the strength of the contraction. Moreover, such devices are useless with obese patients.
Additionally, these devices are too uncomfortable for extended wear by many patients, and may shift due to patient movement thereby producing less accurate readings. The patient's movements are severely restricted, because the transducer must be removed in order for the patient to move any significant distance away from the attached monitor. When the transducer is removed and then replaced on the abdomen, the positioning of the transducer and tension with which it is attached are critical to obtaining repeatable and interpretable results, and must be performed by trained personnel. Even then the results are subject to variation.
Recently, Corometrics Medical Systems, Inc. of Wallingford, Conn. has introduced a guard ring tocotonometer which is purportedly maintained in position on the patient's abdomen with an adhesive baseplate. However, only the cover baseplate is disposable, not the sensor. Moreover, the discomfort occasioned by the plunger-type sensor is not alleviated. Finally, if the patient is to be moved from the vicinity of the monitor, the sensor must be removed and later replaced and readjusted to obtain proper readings.
Another type of device, described in U.S. Pat. No. 4,989,615 to Hochberg, has a soft, fluid-filled bladder element which may be pressurized or internally-supported, depending upon the embodiment. A pressure monitor is disposed to detect changes in pressure in the fluid within the bladder due to the hardening of the abdomen during uterine contractions. This device also requires a belt or body stocking to hold the bladder with some pressure against the patient's abdomen, and is subject to problems similar to those outlined in regard to the guard ring tocotonometers of Smyth and Tweed et al.
Accordingly, a need remains for a non-invasive intra-corporeal movement detector which is attached to a pregnant patient's abdomen without a belt and which overcomes the above-enumerated disadvantages of previous tocotonometers.